JP-2001-355462A, which is a counterpart of U.S. Pat. No. 6,405,694B2, shows a variable valve timing controller in which an actual valve timing is calculated based on a crank angle signal and a cam angle signal. A crank angle sensor outputs the crank angle signal every predetermined crank angle, and a cam angle sensor outputs the cam angle signal every predetermined cam angle. However, in this controller, the actual valve timing cannot be calculated during a period from the time when a previous cam angle signal is outputted until the time when the next cam angle signal is outputted. Thus, even though the actual valve timing is continuously varied, the actual valve timing is stepwise updated.
JP-2004-162706A shows another variable valve timing controller in which a driving motor varies a rotational phase of a camshaft relative to a crankshaft in order to adjust a valve timing. In this valve timing controller, an actual valve timing is calculated based on a cam angle signal and a crank angle signal every when the cam angle signal is outputted from the cam angle sensor. A valve timing varying amount is periodically calculated based on a difference between the driving motor speed and the rotational speed of the camshaft. The valve timing varying amount is added to the actual valve timing which is calculated at the time the cam angle signal is outputted in order to derive a final actual valve timing. Thus, even when the cam angle signal is not outputted, the actual valve timing is periodically calculated to enhance an accuracy of the valve timing controller.
However, in this valve timing controller, a calculation load of the controller is increased, because the actual valve timing is always calculated based on the difference in speeds even when the cam angle signal is not outputted.